Valvoline HM Full Synthetic is a thin oil for its grade. I've experienced low oil pressure with it too at idle in a worn engine that burns some oil. Ironically, I'm running it in two vehicles now, but they're both spec'd for a 20 and I'm using 5W30 since I wanted a bit thicker.
Keep that bottle of PUP clean and pour the ST in it where the care cant see. Then walk into the garage all bow legged and sing "hear comes the good stuff" as you walk up to it. You be surprised how smooth the engine runs after that.
Dont forget to soak the jug un 98.6 degree water so you don't chill the engine as it pours in. you'll hear it go AAAHHHH!!!!!!!!. Pouring cold oil into an engine make it shiver and causes oil leaks..